1. Field of the Invention
A technical field of the present invention relates to a method for manufacturing a semiconductor substrate.
2. Description of the Related Art
In recent years, semiconductor devices formed using an SOI (silicon on insulator) substrate, instead of a bulk silicon substrate, have been developed. By utilizing the features of a thin single crystal silicon layer formed over an insulating layer, transistors in a semiconductor device can be completely isolated from each other, and further, fully depleted transistors can be formed. Accordingly, a semiconductor integrated circuit with high added values such as high integration, high speed driving, and low power consumption can be realized.
As a method for manufacturing an SOI substrate, a so-called hydrogen-ion-implantation separation method is known. A typical process of the method will be described below.
First, hydrogen ions are implanted into a silicon substrate to form a damaged region at a predetermined depth from the surface. Next, a silicon oxide film is formed by oxidation of another silicon substrate which serves as a base substrate. After that, the silicon substrate where the damaged region is formed and the silicon oxide film on the other silicon substrate are firmly attached to each other to bond the two silicon substrates. Then, heat treatment is performed, whereby one of the silicon substrates is separated along the damaged region.
In the aforementioned method, a silicon substrate is used as a base substrate, and as its application, there is a known method for forming a single crystal silicon layer over a glass substrate (for example, see Reference 1). Note that in Reference 1, a separation plane is mechanically polished in order to remove a defect formed by ion implantation or a step on the separation plane.    [Reference 1] Japanese Published Patent Application No. H11-097379